Process for the manufacture of piston rings by powder metallurgy and articles obtained thereby



PROCESS FOR THE MANUFACTURE OF PISTON RINGS BY POWDER METALLURGY AND ARTI- CLES OBTAINED THEREBY h'lax Koehler, Herbede (Ruhr), Germany, assignor to August H. Schilling, Atherton, Calif.

No Drawing. Application December 22, 1950, Serial No. 202,395

9 Claims. (Cl. 29-182) The present invention relates to the manufacture of piston rings for'high speed internal combustion engines based upon the pressing and sintering of mixtures of metallic powders, the main ingredient of which is powdered iron, and containing minor proportions of powdered lead and graphite.

In the known production of objects, for example, piston rings, by the powder metallurgical process, the metal powder is usually subjected to a pressing with a subsequent sintering, that is, a heat treatment wherein the temperature lies considerably under the melting point of the powdered metal mixture. In this type of manufacture, it is well known that the strength of the thus produced sintered body can be increased by the addition of small percentages of manganese, chromium or silicon to the soft iron powder. It has also been attempted to increase the strength of the resultant material by cold-pressing the same subsequent to the sintering or by subjecting it to several sintering treatments. No noteworthy increase in the material strength has, however, been attained by these processes.

Experience has shown, however, that piston rings manufactured according to the above suggestions are not entirely satisfactory for use in high speed internal combustion engines, for the latter impose very high thermal and mechanical stresses upon the rings.

It is the general object of the present invention to provide an improved process for the manufacture of piston rings and other parts for use in engines operating at high speed and at high temperatures.

More specifically, it is an object of the invention to provide an improved process whereby a material suitable for :he manufacture of piston rings for high speed internal :ombustion engines is obtained and in which the crystal ;tructure can be controlled by suitable modifications of the )rocess.

It is a further object of the invention to provide an imroved process for the manufacture of piston ring mate- 'ial by powder metallurgy wherein a mixture containing 'rom 1% to 10% of lead with or without other heavy netals and silicon components all in powdered condition n admixture with powdered iron and a small proporion of powdered graphite, is converted into an extremely trong and heat resistant body, having exceptional bearng qualities by sintering and pressing, and in such man- 161' that the material is given a lamellar pearlitic or a ranular pearlitic or sorbitic structure.

Other objects and advantages of the invention will apear more fully from the following more detailed de- :ription thereof.

According to the present invention, powdered iron is riquetted or preliminarily pressed to approximately the esired final shape after mixing with a small proportion f powdered graphite and with 1% to 10% of powdered :ad which may be replaced in part with one or more other eavy metals (i. e., metals having an atomic weight above with or without silicon, until the specific gravity of re mass is about 6.3 to 6.5. This mass is then sintered 2,741,827 Registered Apr. 17, 1956 at a temperature of about 1000 to 1200 C., depending upon the fusion point of the added metal or metals, for a period of about one to two hours. The mass is then subjected to pres-sure at temperatures and under pressures dependent upon the structure it is desired to create in the finished mass and upon the use to which it is to be put. In all cases, however, the sintered mass is subjected both to high pressure and either simultaneously with the pressing or subsequently thereto is brought to a temperature in the range of about 850 to 1000 C., i. e. above the transition or transformation temperature, after which it is either rapidly quenched, where the material is to be subjected in use to temperatures up to about 300 Clunder load, or it is allowed to cool slowly where it is to be subjected to maximum temperatures of about 200 C. under load.

When additions of other heavy metals such as tin, antimony, manganese, chromium, nickel and copper, and also of silicon, are used along with the lead, the ratio of the additions to the quantity of lead must be so regulated that the diffusion processes internal to the mixed crystalline series structure like high speed internal combustion engines which are operated at a thermally lower stress, where the ring temperatures do not exceed approximately 200 C.

The lamellar pearlitic structure is attained when, in the production of the piston ring material, iron powder containing a small proportion of graphite is mixed with a heavy metal powder consisting entirely or preponderantly of lead, with or without silicon, in the limits of 1 to 10%,

preferably about 5%, which mixture is first pressed to" a specific gravity of approximately 6.3 to 6.5 and then sin tered at 1000 to 1200 C. for one to two hours and sub-. sequently subjected to a hot-pressing at from 900 to 1000" C. and about 85,000 to 100,000 lbs/in. (6,000 to 7,000 kg./cm. with a final slow cooling, for example,

in air or an inert gas.

A lamellar pearlitic structure can also be obtained when the briquette of the above composition (specific weight 6.3 to 6.5) is sintered for from one to two hours at 1000 to 1200 C. followed by a step-wise cold-pressing to a final pressure of about 140,000 lbs/in. (10,000 kg./cm. to a specific weight of 7.6 to 7.7 and with a final heating to 850 to 900 C. for approximately one hour, followed by a slow cooling. This lamellar pearlitic structure is particularly desirable for piston rings for high speed internal combustion engines operating under thermal stresses of the order of approximately 200 C.

For piston rings for high speed internal combustion encedure will give the desirable granular pearlitic or sorbitic structure to the piston ring material.

The above-mentioned mixture is first consolidated to a specific gravity of 6.3 to 6.5, then sintered for one to two hours at 1000 to 1200 C. and subsequently hot-pressed at a temperature 900 to 1000 C. and a pressure of about 85,000 to 100,000 lbs./in. by which a specific gravity of 7.6 to 7.7 is attained. This is followed by a heat treatment at 800 to 850 C. with rapid quenching, for example, in oil. In a modification of my process for attaining this type of material with a granular pearlitic structure, there are carried out the above briquetting and sintering for one to two hours at 1000 to12000 C., and these steps are followed by a step-wise cold-pressing to about 140,000 lbs./in. by which a specific gravity of 7.6 to 7.7 is obtained. After a subsequent heat treatment at 850 to 900 C. for approximately one hour, a rapid quenching is carried out, for example, in oil.

This last described process can be altered in that coldpressing occurs in stages up to pressures of about 210,000 lbs/in. (15,000 kg./cm. and that after a rapid quenching from approximately 800 C. a further soaking occurs at a temperature from 500 to 650 C., in any temperatures lying under the transition point of approximately 720 C. noted:

During the cold-pressing, the cementite as well as the free graphite still present, and the mixed crystals of the Fe-C-heavy metal group, which were formed by the sintering subsequent to the briquetting, are distributed. In consequence, a rapid conversion into martensite is obtained by the subsequent heating to 760 to 820 C. with the rapid quenching that follows. With the subsequent soaking at temperatures of approximately 650 C., a grain structure build-up results whose special characteristic is annealed sorbite. This gives to the material the characteristics which are valuable for piston rings; namely, a higher elastic limit, strength and a springiness as well as extremely good running and slipping characteristics as yet not attained by any other process. The length of time required by the soaking must be determined by the cross section of the material and the desired strength; the time increases with larger cross sections and for the reaching of higher strengths.

The following example will serve to illustrate the invention more specifically without, however, indicating the limits thereof.

In further explanation the following may be Example I The following materials were mixed together:

Percent Powdered iron 93 Powdered graphite (ash content 1.5 Powdered lead with additives 4.5

which mixture had the following approximate grain size distribution:

Percent under 0.06 mm between 0.06 and 0.1 mm 39 between 0.1 and 0.2 mm 26 over 0.2 mm 15 The initial pressing or briquetting of this material occurred at a pressure of about 70,000 lbs./in. (4,900 kg./cm. followed by sintering at approximately 1100 C. for two hours in a neutral furnace atmosphere. This crude sintered mass had a porosity of approximately 23% and an ultimate strength of 14,000 to 17,000 lbs/in. (10 to 12 kg./m.m.

This material was subsequently pressed at a temper-- ature of 1000 C. and a pressure of about 100,000 lbs./in. the temperature having been attained in a pro tective atmosphere, and the material then allowed to cool slowly. This material had a definite fine lamellar pearlitic structure and the characteristics tabulated below under the heading Example I.

Example 11 The same mixture as in Example I, after sintering, was cold-pressed in stages until a maximum pressure of about 140,000 lbs/in. (9,800 kg./cm. was reached. This material was subsequently heated and held for one hour at a temperature of 850 C. (The effect attained by this Example I Example II Elastic limit, kg./mrn. 57.5 (82,000 lbs./

Ultimate strength, kg./mm. 76.5 (109,000 lbs./

ill.

Elongation Cheriical Analysis:

62.6 (89,000 lbs./

in. 74.5 (106,000 1bs./

72; remainder prox. 94.7%).

. remainder (approx.

While in the foregoing, I have referred specifically to iron as the ferrous component, it will be understood that various suitable types of steel can be employed, in place of various forms of iron, suitable adjustment of the quantity of graphite being made where necessary.

The term heavy metal or heavy metal powder as employed in the specification and claims is to be understood as having reference to a solid metal of an atomic weight above 50 and of the type commonly employed in the metallurgy of iron and steel, and in minor proportions with reference to the iron, in order to modify the properties of the essentially ferrous product. The lead, tin, antimony, manganese, chromium, nickel, and copper referred to hereinabove are typical examples of additions in modified iron and steel products and ferrous alloys.

I claim:

1. In a process for the manufacture of piston rings by powder metallurgy and suitable for use in high speed internal combustion engines, the steps which include pressing a mixture comprising a preponderating proportion of iron powder, about 1 to 10% of lead powder, and a small proportion of graphite to approximately the desired shape, sintering the mass, and subsequently hot-pressing the same.

2. Process according to claim 1 including the subsequent step of slowly cooling the mass from an elevated temperature to produce a lamellar pearlitic structure.

3. Process according to claim 1, including the subsequent step of quenching the mass from an elevated tem perature to produce a granular structure of the type of pearlite and sorbite.

4. In a process for the manufacture of piston rings by powder metallurgy and suitable for use in high speed internal combustion engines, the steps which include pressing a mixture comprising a' preponderating proportion of iron powder, about 1 to 10% of lead powder, and about 1.5% of graphite, to a specific weight of about 6.3 to 6.5, sintering the mass at about 1,000 to 1200 C., subsequently again pressing the mass at a temperature of about 900 to 1,000 at a pressure of about 85,000 to 100,000 lbs./in. and quenching the pressed mass in a liquid from a temperature of about 800 to 850 C.

5. A sintered piston ring composed principally of iron and containing 1 to 10% of lead, at least part of the lead being in the form of an iron-lead-carbon alloy, the carbon content being of the order of about .5%.

6. A quenched, sintered piston ring composed principally of iron and containing 1 to 10% of lead and having a granular structure of the type of pearlite and sorbite, at least part of the lead being in the form of an iron-lead-carbon alloy, the carbon content being of the order of about .5

7. A sintered piston ring composed principally of iron and containing about 0.48 to 0.52% of carbon, 3.45 to 3.55% of lead, 0.36 to 0.41% of tin and 0.45 to 0.52% of copper, the ring having an elastic limit of about 82,000 to 89,000 lbs./in. an ultimate strength of about 106,000 to 109,000 lbs./in. and an elongation of 1.5 to 2, at least part of the lead being in the form of an iron-lead-carbonalloy.

8. A substantially non-porous sintered piston ring cornposed principally of iron and containing 1 to of lead which at least in part is in the form of an iron-lead-carbon alloy, with a small quantity of at least one member of the group consisting of tin, antimony, manganese, chromium, nickel, copper and silicon, said ring having a lamellar pearlitic structure and a specific gravity of 7.6 to 7.7.

9. A substantially non-porous sintered piston ring composed principally of iron and containing 1 to 10% of lead which at least in part is in the form of an iron-lead-carbon alloy, with a small quantity of at least one member of the group consisting of tin, antimony, manganese, chromium, nickel, copper and silicon, said ring having a granular structure of the type of pearlite and sorbite and a specific gravity of 7.6 to 7.7.

6 1,974,173 Calkins Sept. 18, 1934 2,192,792 Kurtz Mar. 5, 1940 2,214,104 Hildabolt et a1 Sept. 10, 1940 2,275,420 Clark et al. Mar. 10, 1942 2,319,373 Tormyn May 18, 1943 2,327,805 Koehring Aug. 24, 1943 2,342,799 Goetzel Feb. 29, 1944 2,386,604 Goetzel Oct. 9, 1945 2,401,483 Hensel June 4, 1946 2,409,307 Patch et a1 Oct. 15, 1946 2,411,073 Whitney Nov. 12, 1946 2,435,511 Rice Feb. 3, 1948 2,518,253 Reis Aug. 8, 1950 FOREIGN PATENTS 609,689 Great Britain Oct. 5, 1948 625,397 Great Britain June 27, 1949 OTHER REFERENCES Metal Powder Report, I, 1947, pages and 89.

Powder Metallurgy by H. H. Hausner, page 128 (Table 41), published 1947 Chemical Publishing Co. (Brooklyn, N. Y.)

Goetzel: Treatise on Powder Metallurgy, Interscience Publishers, New York city, 1950, vol. 2, pages 522-523. 

1. IN A PROCESS FOR THE MANUFACTURE OF PISTON RINGS BY POWDER METALLURGH AND SUITABLE FOR USE IN HIGH SPEED INTERNAL COMBUSTION ENGINES, THE STEPS WHICH INCLUDE PRESSING A MIXTURE COMPRISING A PREPONDERATING PROPORTION OF IRON POWDER, ABOUT 1 TO 10% OF LEAD POWDER, AND A SMALL PROPORTION OF GRAPHITE TO APPROXIMATELY THE DESIRED SHAPE, SINTERING THE MASS, AND SUBSEQUENTLY HOT-PRESSING THE SAME. 